Send copy to & Autoresponder not working

I've having a problem with Send copy to and the autoresponder. They simply are not working for all domains. I can send and receive emails no problem. The email forwarding is working no problem (if it's related). I'm running the latest version of ISP Config 3 (3.0.5.1).

Any ideas what I can check? The mail log looks fine but there is no indication that the copy is being sent or that the autoresponder failed in some way.

Copy to (optional) is not working. (There is a separate function called email forward which is working.) One of my clients wants to use this functionality so it would be nice to get it working. The autoresponder is not so important currently.

Check that the settings under System > server config > mail are correct. especially the imap server type and the filter language must match the software installed on your server.

Click to expand...

For sure they're set to the correct things but it is possible that the courier-maildrop package wasn't installed at the very beginning. It has been for a few weeks already now. Is there configuration I need to edit?

EDIT: Although the package maildrop was installed since the beginning. By the looks of it this is the package that is needed so I just removed the courier-maildrop package. Still not working though...